C++面向对象程序设计双语教程（第3版）课件 class 14-template

ObjectivesTounderstandthepurposeofgenericprogrammingToknowthemechanismoftemplatesTobeabletodefinefunctiontemplatesandinstantiatefunctiontemplatesTobeabletodefineclasstemplatesandinstantiateclasstemplates01IntroductiontoTemplates04ClassTemplates02FunctionTemplates03FunctionTemplateInstantiation05ClassTemplateInstantiation01IntroductiontoTemplatesWhatisaTemplate?Imaginethatwewanttowriteafunctiontofindthemaximumoneoftwovalues.Inpractice,we’dwanttodefineseveralsuchfunctions,eachofwhichwillfindthemaximumvalueofagiventype.CasestudyintmaxV(int

x,int

y){return(x>y)?x:y;}charmaxV(char

x,char

y){return(x>y)?x:y;}doublemaxV(double

x,double

y){return(x>y)?x:y;}#definemaxV(x,

y)((x>y)?x:y)Problem:Macropresentsthepossibilityforserioussideeffects:notypechecking,repetitiveoperationsandsoon.intmain(){inti=5,j=3;cout<<maxV(++i,j);return0;}Result:7TmaxV(Tx,Ty){return(x>y)?x:y;}Result:6TheConceptofTemplatesTemplatemechanismallowsatypetobeaparameterinthedefinitionofaclassorafunction.TmaxV(Tx,Ty){return(x>y)?x:y;}Templatesprovideasimplewaytorepresentawiderangeofgenericconceptsandsimplewaystocombinethem.Templatesarethefoundationforgenericprogramming.Atemplateisablueprintorformulaforcreatingclassesorfunctions.

TemplatesareoneofC++’scapabilitiesforsoftwarereusability.02FunctionTemplatesFunctionTemplatestemplate<typenameidentifier>,ortemplate<classidentifier>function_declaration(orfunction_definition);template<classT>TmaxV(Tx,Ty){return(x>y)?x:y;}Keywordtemplate<typenameT>TmaxV(Tx,Ty){return(x>y)?x:y;}typeidentifierintmaxV(int

x,int

y){return(x>y)?x:y;}charmaxV(char

x,char

y){return(x>y)?x:y;}doublemaxV(double

x,double

y){return(x>y)?x:y;}templateparameterlistkeywordCasestudySyntaxtodefineafunctiontemplateFunctionTemplatesAfunctiontemplatedefinesafamilyoffunctionsthatcanoperatewith

generictypes.Thisallowsustocreateafunctiontemplatewhosefunctionalitycanbeadaptedtomorethanonetypewithoutrepeatingtheentirecodeforeachtype.03FunctionTemplateInstantiationFunctionTemplatesInstantiationtemplate<typename

T>TmaxV(Tx,Ty);//declarationintmain(){cout<<maxV(3,4)<<endl;cout<<maxV(3.4,67.8)<<endl;cout<<maxV('s','x')<<endl;return0;}template<typename

T>//definitionTmaxV(T

x,T

y){return(x>y)?x:y;}Functiontemplateinstantiationfunction_name<type>(arguments);cout<<maxV<int>(3,4);cout<<maxV<double>(3.4,67.8);cout<<maxV<char>('s','x')Functiontemplateinstantiationisacreationof

aconcretefunction.FunctionTemplatesInstantiationWhenwecallafunctiontemplate,thecompiler(ordinarily)usestheargumentsofthecalltodeducethetemplateparameter(s)(T)forus.cout<<maxV(3,4)<<endl;cout<<maxV(3.4,67.8)<<endl;cout<<maxV('s','x')<<endl;Nocodeisgeneratedfromasourcefilethatcontainsonlytemplatedefinitions.Inorderforanycodetoappear,atemplatemustbeinstantiated:thetemplateargumentsmustbedeterminedsothatthecompilercangenerateanactualfunction.FunctionTemplateswithdifferentTypeParameterstemplate<typename

T1,typename

T2>T1getMin(T1

x,T2

y){return

x<y?x:(T1)y;}intmain(){inti=9,j=6;doublea=8.3,b=7.8;cout<<getMin(i,a);return0;}cout<<getMin<int,double>(i,a);template<typename

T1,T2>//errorT1getMin(T1

x,T2

y){return

x<y?x:(T1)y;}FunctionTemplatesandOverloadingBothoftheymakecodesmorecompactandconvenient.Functionoverloadingisnormallyusedtoperformsimilaroridenticaloperationsondifferenttypesofdata.Functiontemplates

areusedtoperformidenticaloperationsondifferenttypesofdata.FunctionTemplates

Overloadingtemplate<typename

T>voidSwap(T&x,T&y);voidSwap(int&x,int&y);intmain(){inti=9,j=6;doublea=8.3,b=7.8;chars='4',t='5';Swap(i,j);Swap(a,b);Swap(s,t);return0;}template<typename

T>voidSwap(T&x,T&y){Ttemp;temp=x;x=y;y=temp;cout<<"Calloftemplate\n";}voidSwap(int&x,int&y){inttemp;temp=x;x=y;y=x;cout<<"Calloffunction\n";}Result:CalloffunctionCalloftemplateCalloftemplateWhenanon-templatefunctionprovidesanequallygoodmatchforacallasafunctiontemplate,thenon-templateversionispreferred.FunctionTemplates

OverloadingTemplate<typenameT>TgetMin(Tp1,Tp2);TgetMin(Tp1,Tp2,Tp3);Template<typenameT>TgetMin(Tp1,Tp2);intgetMin(intp1,intp2);Wecandeclareseveralfunctiontemplateswiththesamenameandevendeclareacombinationoffunctiontemplatesandordinaryfunctionswiththesamename.Thecompileralwaysmatchesfirstfunctionprototypes(exactlymatching),andthenfunctiontemplates.FunctionTemplates

Overloadingtemplate<typenameT>TgetMax(Tx,Ty){cout<<"callingtemplate\n";return(x>y)?x:y;}intgetMax(inti,intj){cout<<"callingafunctionwithinttype\n";return(i>j)?i:j;}intgetMax(doubled,inti){cout<<"callingafunctionwithadoubletype\n";return(d>i)?(int)d:i;}constintn=7;intmain(){inti=5,j=6;doublea=8.3,b=7.8;charc1='a',c2='b';cout<<getMax(i,j)<<endl;cout<<getMax(c1,c2)<<endl;cout<<getMax(a,b)<<endl;cout<<getMax(n,i)<<endl;cout<<getMax('a',1)<<endl;cout<<getMax(2.7,4)<<endl;return0;}123112232FunctionTemplatesResult:callingafunctionwithinttype6callingtemplatebcallingtemplate8.3callingafunctionwithinttype7callingafunctionwithinttype97callingafunctionwithadoubletype404ClassTemplatesClassTemplatesStackisakindofdatastructurewithLIFO(lastin,firstout).Ithastwoprincipaloperations:pushandpop.CasestudyStack+Stack()+~Stack()-IsEmpty():bool-IsFull():bool+push(int&):void+pop():int+peak():int+getSize():intconst-element:int*size:intconst-top:intClassTemplatesclass

Stack{public:Stack();~Stack();voidpush(int&i);intpop();

intpeak();intgetSize()const;private:boolIsEmpty();boolIsFull();const

intsize;int*element;inttop;};Stack+Stack()+~Stack()-IsEmpty():bool-IsFull():bool+push(int&):void+pop():int+peak():int+getSize():intconst-element:int*size:intconst-top:intStack::Stack():size(5),top(0){element=new

int[size];}Stack::~Stack(){delete[]element;}bool

Stack::IsEmpty(){return--top==-1;}bool

Stack::IsFull(){returntop>=size?true:false;}void

Stack::push(int&i){if(!IsFull())element[top++]=i;elsethrow-1;}int

Stack::pop(){if(IsEmpty())throw-2;returnelement[top];}int

Stack::peak(){returnelement[top-1];}int

Stack::getSize()const{returntop;}ClassTemplatesintmain(){Stackst;try{for(inti=0;i<4;i++)st.push(i);cout<<

"----------------\n";cout<<st.getSize()<<st.peak()<<endl;intnum=st.getSize()+1;for(inti=0;i<num;i++)cout<<st.pop()<<

"";}catch(inte){if(e==-1)cout<<

"Thestackisfull.\n";if(e==-2)cout<<

"Thestackisempty.\n";}}template<typename

T>class

Stack{public:Stack();~Stack();voidpush(T&i);Tpop();Tpeak();intgetSize()const;private:boolIsEmpty();boolIsFull();const

intsize;T*element;inttop;};Definitionof

aClassTemplatetemplate<classT>Tisagenerictype(typeparameter)Defineaclassasatemplate.Thisclassiscalledclasstemplate.Typeparameterintheclassmaybedatamembers,andmemberfunctions’parameters,andreturningvalueClassTemplatetemplate<typename

T>Stack<T>::Stack():size(5),top(0){element=new

T[size];}template<typename

T>Stack<T>::~Stack(){delete[]element;}template<typename

T>bool

Stack<T>::IsEmpty(){return--top==-1;}template<typename

T>bool

Stack<T>::IsFull(){returntop<size?true:false;}template<typename

T>void

Stack<T>::push(T&i){if(IsFull())element[top++]=i;elsethrow-1;}template<typename

T>T

Stack<T>::pop(){if(IsEmpty())throw-2;returnelement[top];}template<typename

T>T

Stack<T>::peak(){returnelement[top-1];}template<typename

T>int

Stack<T>::getSize()const{returntop;}05ClassTemplateInstantiationClassTemplateInstantiationintmain(){Stack<int>st;try{for(inti=0;i<4;i++)st.push(i);cout<<

"----------------\n";cout<<st.getSize()<<st.peak()<<endl;intnum=st.getSize()+1;for(inti=0;i<num;i++)cout<<st.pop()<<

"";}catch(inte){if(e==-1)cout<<

"Thestackisfull.\n";if(e==-2)cout<<

"Thestackisempty.\n";}}Classtemplateisinstantiated.st

isatemplateclassobjectTheprocessofgeneratingaconcreteclassfromatemplatedefinitionandtemplateargumentsisoftencalledclass

templateinstantiation.ClassTemplateInstantiationclass

A{public:A()=default;A(int

x):a(x){}friend

ostream&operator<<(ostream&o,A&obj){o<<obj.a;

returno;}private:inta;};intmain(){Stack<A>stObj;try{cout<<

"objectsarepushedintoastackonebyone.\n";for(inti=0;i<4;i++){Aobj=A(i);stObj.push(obj);}Aobj=stObj.peak();cout<<stObj.getSize()<<obj<<endl;cout<<

"objectsarepopedfromastackonebyone.\n";intnum=stObj.getSize()+1;for(inti=0;i<num;i++){Atemp=stObj.pop();cout<<temp;}}catch(inte){if(e==-1)cout<<

"Thestackisfull.\n";if(e==-2)cout<<

"Thestackisempty.\n";}}DefinitionofClassTemplateA<T>-a:T+A(T)+operator+(A<T>&):A<T>&<<C++Global>>+operator<<(ostream&,A<T>&):ostream&+operator>>(istream&,A<T>&):istream&<<C++Friend>>template<typename

T>class

A{public:A(T);A<T>&operator+(A<T>&);friend

ostream&operator<<(ostream&out,A<T>&obj){out<<obj.a<<endl;return

out;}friend

istream&operator>>(istream&in,A<T>&obj){in>>obj.a;return

in;}private:Ta;};ClassTemplateInstantiationtemplate<typename

T>A<T>::A(T

type){a=type;}template<typename

T>A<T>&A<T>::operator+(A<T>&obj){a=a+obj.a;return*this;}intmain(){A<int>intA1(10),intA2(20);cout<<intA1+intA2;cout<<intA2;

A<char>charA(''),charB('');cin>>charA;cin>>charB;cout<<charA+charB;

return0;}Eachinstantiationofaclasstemplateconstitutesanindependentclass.Non-TypeParametersforTemplatestemplate<typename

T,intN>class

mysequence{Tmemblock[N];public:voidsetMember(intx,Tvalue);TgetMember(intx);};template<typename

T,intN>void

mysequence<T,N>::setMem